Control of structural phase transition and energy storage behavior through cooling rate in (Bi_0.5Na_0.5)TiO₃-BaTiO₃ ceramics

In lead-free (Bi_0.5Na_0.5)TiO₃-BaTiO₃ (BNT-BT) ceramics, the BNT-rich side has R3c ferroelectric domains at room temperature, and modulated P4bm tetragonal nanodomains develop within the R3c rhombohedral phase at approximately the depolarization temperature T_d. Such structural phase transitions have conventionally been modulated by doping with additives or by controlling the composition. However, it is considered that the coexistence region between the R3c and P4bm phases is important for enhancing the energy storage behavior because the phase reversal between them, caused by the electric field, can cause the BNT-based ceramics to exhibit an antiferroelectric-like pinched hysteresis loop. In this study, the structural phase transition of BNT-BT ceramics is promoted through process control, that is, by adjusting the cooling rate, and then the stabilization of the P4bm phase and the expansion of the coexistence region of the R3c and P4bm phases were examined, which results in enhanced energy storage behavior. Consequently, BNT-BT ceramics prepared at a slower cooling rate (0.01 °C s⁻¹) than that of normal firing (0.05 °C s⁻¹) demonstrate the stabilization of the P4bm phase and expansion of the coexistence region of the R3c and P4bm phases. Therefore, process control modulates the structural phase transition, which can cause enhanced energy storage behavior.